• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
• | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
• | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
ECT Sensor Signal | P0117 | P0118 | P0118 | P0116, P0128 |
Low Reference | -- | P0118 | P0118 | P0128 |
Circuit | Short to Ground | Open | Short to Voltage |
---|---|---|---|
Parameter Normal Range: -39 to +149°C (-38 to +300°F) | |||
ECT Sensor 1 Signal | 149°C (300°F) | -40°C (-40°F) | -40°C (-40°F) |
Low Reference | -- | -40°C (-40°F) | -40°C (-40°F) |
The engine control module (ECM) uses this diagnostic to determine if the engine coolant temperature (ECT) has reached the minimum calibrated thermostat regulating temperature. The ECM supplies 5 volts to the ECT signal circuit , and a ground for the ECT low reference circuit. The ECM monitors the temperature of the coolant by using the input received from the ECT sensor. The ECM calculates the amount of fuel burned since start-up to determine if the vehicle has been driven within the conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally, or does not reach the regulating temperature of the thermostat, the engine is considered not warm enough for stable, low emission operation.
The purpose of this rationality diagnostics is to use the ECT sensor to determine if the engine coolant will heat up at the correct rate, and also meet the calibrated target temperatures under various operating conditions.
The ECM uses the start-up ECT and the start-up intake air temperature (IAT) to begin the diagnostic calculation.
• | DTCs P0112, P0113, P0116, P0117, P0118 are not set. |
• | The engine is running. |
• | The IAT 1 is colder than 10°C (50°F), low region. |
• | The IAT 1 is warmer than 10°C (50°F), high region. |
• | The start-up engine coolant temperature is colder than 51°C (124°F). |
• | DTC P0128 will only run once per ignition cycle until a Pass, Fail or Disable condition exists. |
The engine did not meet the ECT target temperatures of 50°C (120°F) low region or 72°C (162°F) high region during expected calibrated warm-up times and start-up temperatures.
DTC P0128 is a Type B DTC.
DTC P0128 is a Type B DTC.
• | DTC P0128 occurring with insufficient vehicle interior heating is an indication of improper thermostat operation. |
• | Inspect the ECT sensor terminals and the ECT harness connector for corrosion. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT. |
• | This diagnostic runs in a specific range. Measure and record the resistance of the ECT sensor at various ambient temperatures between -7 to +80°C (+19 to +176°F), then compare those measurements to the Temperature Versus Resistance table. |
• | A slight to moderate resistance in the ECT sensor signal circuit or low reference circuit will affect this diagnostic. This condition results in a greater voltage on the ECT sensor signal circuit, which is interpreted by the ECM as a colder ECT. |
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Control Module References for scan tool information
Important: A critical analysis of the operation of the thermostat is necessary to properly diagnose this DTC.
⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM. |
⇒ | If greater than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM. |
⇒ | If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM. |
• | Measure and record the resistance of the ECT sensor at various ambient temperatures and compare those measurements to the Temperature vs. Resistance table. Refer to Temperature Versus Resistance. |
• | Refer to Thermostat Diagnosis. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• | Control Module References for ECM replacement, setup, and programming |